The invention relates to a device for a flotation machine, particularly to a bearing assembly of a drive shaft of the flotation machine. The bearing assembly contains one or more bearings and an air transfer chamber separated from the bearing or bearings.
In a flotation machine a drive shaft is used to support the submerged mechanism which mixes slurry as well as for feeding air to the flotation machine. Then the drive shaft is hollow so that air is transferred inside the drive shaft to the rotor installed on the end of the drive shaft. By mixing and air feeding a part of the slurry containing for instance desired valuable metal or minerals is flotated and this flotated part of the slurry is removed from the flotation cell as an overflow via a froth lip in the upper part of the flotation cell. The non-flotated part of the slurry is removed from the flotation cell for instance through a bottom outlet of the flotation cell. Slurry is fed into the flotation cell in an essentially continuous fashion so that slurry to be fed will replace flotated and non-flotated parts removed from the flotation cell.
The drive shaft of the flotation machine has a bearing housing which is usually manufactured as a single casting. The casting of the bearing housing is then machined out to take the bearings and lip seals so that the air transfer chamber is between the bearings and the lip seals in the same casting. Thus the bearings, the lip seals and the air transfer chamber are combined with each other. When a bearing or a lip seal is needed to be changed the whole combination of the bearings, the lips seals and the air transfer chamber have to be removed from the drive shaft. Further, because the assembly of the bearing housing is difficult and requires a person well trained in the art, the maintenance of the bearing assembly will be expensive and takes time.
The object of the present invention is to eliminate some drawbacks of the prior art and to achieve a new device for the bearing assembly of the drive shaft in a flotation machine which device is simpler as its construction and easier and cheaper to maintain. The essential features of the invention are enlisted in the enclosed claims.
According to the invention a drive shaft for a flotation machine is used for mixing and transporting the air to a rotor in the flotation cell of the flotation machine. The drive shaft is advantageously provided with a rotor at that end of the drive shaft which is submerged in the slurry in the flotation cell. At the end or in the vicinity of the end of the drive shaft opposite to the end submerged in the slurry the drive shaft is connected with a drive arrangement. The drive shaft is driven by the drive arrangement for mixing the slurry in the flotation cell. Air to be used in the flotation process for forming froth in the flotation cell is fed through the drive shaft so that air is dispersed into slurry via the rotor blades. The drive shaft is thus hollow in its interior at least in that part where air is transported to the rotor. In order to stabilise the drive shaft for slurry mixing the drive shaft is provided with at least one bearing, advantageously in the vicinity of the drive arrangement.
In the preferred embodiment of the invention the drive shaft of the flotation machine is provided with two bearings installed in the vicinity of the drive arrangement. The bearings have separate bearing housings. Between these bearing housings a separate air transfer chamber is installed around the drive shaft. The air transfer chamber is used to feed air from an external source to the interior of the drive shaft. The air transfer chamber is formed so that concentrically around the drive shaft there is installed at least one element which is sealed around the drive shaft at both ends by seals so that the inner diameter of the element is essentially the same as the outer diameter of the drive shaft in the ends or in the vicinity of the ends of the element. Space for air in the air transfer chamber is formed so that the inner diameter of the element is greater than the outer diameter of the drive shaft on the area between the ends of the element. The air transfer chamber is provided with at least one connecting member which has connection with the external source of air. Because the air transfer chamber is separated from the bearings the air transfer chamber is removable and independent from the use or lifetime of the bearing housings.
For preferred air feeding in accordance with the invention, the drive shaft is provided with at least one opening between the external surface of the drive shaft and the interior of the drive shaft. This opening is so positioned and shaped that the opening has contact with the air transfer chamber essentially continuously in order to create a closed air feeding from the external air source to the rotor of the flotation machine. Thus air to be fed to the rotor is first flowed into the air transfer chamber and, thereafter, into the interior of the drive shaft and further through the rotor as dispersed bubbles into the slurry in the flotation machine.
The element forming the air transfer chamber is preferably installed in a non-fixed position to the drive shaft so that the element can be rotated between 0 and 360 degrees around the drive shaft. In one embodiment the element can also be installed so that the element is rotated with the drive shaft and the opening between the air transfer chamber and the interior of the drive shaft is kept essentially at the same position to the air transfer chamber. Then the opening can be a relatively small hole in the drive shaft, and the air transfer chamber can be shaped smaller and narrower, like a ring with a connecting member for feeding air into the interior of the drive shaft. Independent from the shape of the opening the opening has to be such that the opening allows a continuous air flow from the air transfer chamber into the interior of the drive shaft.
Using the device of the invention the initial assembly of the bearings is easier and cost effective and the maintenance is much easier to the prior art because the bearings and the air transfer chamber can be installed and changed separately. This also means that the bearing housing and the air transfer chamber can be rotated between 0 and 360 degrees around the drive shaft and thus advantageously the air transfer chamber can be installed in different positions to the bearings. The bearings can also be rotated around the drive shaft when installed in order to ensure that the bearing clearances are correct. The device of the invention eliminates the use of withdrawal sleeves and further simplifies the bearing assembly. Naturally, it is also possible to install at least one bearing housing and the air transfer chamber so that the bearing housing and the air transfer chamber are not able to rotate around the drive shaft and thus the bearing housing and the air transfer chamber are fixed to the drive shaft.